The present invention relates to a copying machine and, more particularly, to a drive system for a thermal fixing roller employed in a copying machine.
Generally, a thermal fixing roller system includes a pair of rollers. One of the rollers is a heater roller within which a heater is disposed to heat the heater roller to a desired temperature suited for the thermal fixing operation. The other roller is a pressure roller which contacts the heater roller and creates a predetermined pressure against the heater roller. A copy paper carrying a toner image thereon is driven to travel between the heater roller and the pressure roller in such a manner that the toner image contacts the heater roller, whereby the toner image is thermally fixed while the copy paper travels through the thermal fixing roller system. The pair of rollers are driven to rotate while the fixing operation is conducted.
In the conventional thermal fixing roller system, when the main power supply is initiated, the heater disposed in the heater roller is energized to heat up the heater roller to a preselected temperature. When the heater roller reaches the preselected temperature after the above-mentioned preparation period, a ready lamp is activated and the copying operation is conducted in response to the actuation of the copy button. During the preparation period, a pair of rollers in the thermal fixing roller system are not driven to rotate to minimize the power dissipation. A temperature sensor is provided for detecting the surface temperature of the heater roller, and a control circuit is connected to the heater so as to maintain the surface temperature of the heater roller within a predetermined range.
As discussed above, in the conventional system, the heater roller and the pressure roller do not rotate during the preparation period. The pressure roller contacts the heater roller at a fixed position. Thus, the pressure roller is maintained at the ambient temperature except for the fixed position which contacts the heater roller. Under these conditions when the pair of rollers are driven to rotate in response to the actuation of the copy button, great amount of heat energy is absorbed by the pressure roller. The surface temperature of the heater roller is reduced and, therefore, the heater disposed in the heater roller is energized to heat up the heater roller. This recovering operation takes a considerably long period if the ambient temperature is low or the power supply voltage level is low. It will be clear that a desired fixing operation is not achieved until the heater roller is again heated up to the preselected temperature.
Accordingly, an object of the present invention is to provide a novel thermal fixing roller system which ensures a stable fixing operation.
Another object of the present invention is to maintain both of the heater roller and the pressure roller at a preselected temperature before initiating the actual copying operation.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, the heater roller and the pressure roller are driven to rotate during the preparation period. Accordingly, when the heater roller reaches the preselected temperature and the ready lamp is energized, the heat energy flowing from the heater roller to the pressure roller is negligible when the pair of rollers are rotated in response to the actuation of the copy button.